1. Field of the Invention
This invention relates to conference rooms having sound pick-up and sound amplification systems. More particularly, the invention pertains to conference room installations which include one or more microphones for picking up the voices of human participants and one or more loudspeakers driven by electronic amplifiers, either to ensure that all participants can adequately hear the remarks of one speaking participant, or for communication with distant persons over telephone or intercom lines. Specifically, the invention relates to a method and apparatus for alleviating sound-coupled feedback from the loudspeaker(s) to the microphone(s), which has been a long-standing problem observed in the use of such conference room sound systems.
2. Description of the Prior Art
(Prior Art Statement Under Rule 97)
U.S. Pat Nos. 2,580,439 (Kock, 1952); 3,992,586 (Jaffe, 1976) and 4,078,155 (Botros et al, 1976) all disclose sound systems that could be used in conference rooms and recognize feedback from loudspeakers to microphones as a plaguing problem. Jaffe teaches that the loudspeakers should direct their emitted sound toward the participants, and preferably the microphones should be located equidistant from loudspeakers driven 180.degree. out-of-phase so as to produce nulls at the locations of the microphones. The severity of the feedback problem is illustrated by the effort in designing electronic circuitry to deal with it. See U.S. Pat. Nos. 2,736,771 (Hanson), 3,588,352 (Yamawaki) and 3,784,747 (Berkley et al).
U.S. Pat. No. Des. 154,143 (Reed) issued June 14, 1949, shows loudspeakers placed underneath the top of a table, presumably for outputting music or radio entertainment programs, but with no microphone involved and thus no feedback problem.